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Abstract
Existing research on policy diffusion focuses almost exclusively on "successes" where many jurisdictions adopted the policy or policies under examination. Some have speculated that this "pro-innovation bias" compromises scholars' ability to draw valid inferences about the factors that influence the diffusion process. We argue that the study of interstate compacts in the United States provides an analytic opportunity to assess whether these concerns are warranted because it allows us to examine an entire universe of cases with unusually wide variability in their adoption patterns. Based on a pooled event history analysis of the interstate compacts that are open to all fifty states, we conclude that the tendency to limit diffusion research to widely adopted policies affects the results of previous studies. Specifically, it appears to lead scholars to systematically overestimate the impact of geographic diffusion pressures and policy attributes, and to underestimate the importance of professional associations and the opportunity to learn from previous adoptions. In sum, the longstanding concerns about a pro-innovation bias in diffusion research seem to be warranted.
Keywords
policy diffusion, state politics, interstate compacts, selection bias, complexity, professional associations
The process through which political phenomena spread from one jurisdiction to another, typically called diffusion, is a central concern in political science. By one count, political science journals have published nearly eight hundred articles on the subject, with over half of them appearing within the last decade (Graham, Shipan, and Volden 2013). Interest in diffusion cuts across virtually every subfield of the discipline. Scholars of comparative politics, international relations, and American politics have examined the diffusion of democracy (Brinks and Coppedge 2006), international norms about human rights (Keck and Sikkink 1998), pension and health care reform (Weyland 2006), political institutions (Bridges 1997), and many other political phenomena. Few topics have simultaneously engaged so many scholars in so many disparate areas of the discipline.
The recent proliferation of diffusion research has produced numerous theoretical, methodological, and empirical advances (Graham, Shipan, and Volden 2013). Despite these impressive gains, however, some have speculated that existing studies suffer from a "pro-innovation bias" because they examine only episodes during which an innovation was adopted by a large number of jurisdictions (Rogers 1995). According to these critics, constructing a compelling account of why diffusion occurs, or...